I. Field of the Invention
The present invention is directed generally to the iontophoretic transport of ions for therapeutic purposes. More particularly, it involves the use of a direct current stimulus to transport cardioactive drugs such as antiarrhythmia, vasodilators, inotropic drugs to cardiac tissue.
II. Discussion of the Related Art
Implantable defibrillator devices have been under development and use for some time. This device is used for the correction of either ventricular tachycardia (abnormally rapid heart rate) or ventricular fibrillation (an extremely rapid heart beat disorder) by discharging electrical energy into the heart normally between internally placed electrodes. The electrode arrangement may include two large patches which are placed on the epicardial or pericardial surface adjacent the heart tissue. When the implantable defibrillator senses or recognizes ventricular tachycardia or fibrillation the implantable defibrillator discharges, normally with about 30 joules of electrical energy via the two patches. The current utilized for the devices is supplied by a battery powered pulse generator implanted under the skin of the patient.
Ventricular arrhythmias in patients with coronary heart disease and myocardial infarction probably originate from the areas of slow conduction within the previously infarcted myocardium region. Most patients with sustained monomorphic ventricular tachycardia have various degrees of myocardial scar secondary to obstructed coronary arteries.
The efficacy of antiarrhythmic medication is related to concentration of the drug at the arrhythmogenic area. Since most antiarrhythmic drugs require high myocardial tissue concentrates to be effective, high dose intake of such drugs will lead to high plasma concentrations and with it high incidence of toxic side effects.
Iontophoretic transport of ions is a technique in which positive or negative ions are driven into tissue of interest by current applied between two electrodes one of which contains a supply of the material to be transported. Iontophoresis for therapeutic purposes by means of a direct current was introduced in 1908 by Leduc. Since then it has been introduced in several fields such as transdermal delivery of steroids to joints, as well as transdermal delivery of local anesthetics, facilitated transdermal transport of insulin, and the like.
A system which provides for the subcutaneous injection of a drug into an implanted reservoir connected to the heart by a pacer lead is described in U.S. Pat. No. 4,774,951 to Osypka. Other references teach the delivery of drugs to a treatment site through techniques and methods such as porous electrode leads, by dissolving slowly from an immobilized site, or by osmosis through a permeable membrane.